In recent years, with the strengthening of exhaust regulation, in engines, suppression of the total amount of unburnt particles (PM: Particulate Matter) during mode running and suppression of the number of unburned particles (PN: Particulate Number) which is the number thereof are required, so that a fuel injection device capable of controlling a minute injection amount is required. As a means for suppressing the generation of unburned particles, it is effective to inject the fuel spray during one combustion stroke dividedly into a plurality of times (hereinafter referred to as split injection). By performing split injection, adhesion of fuel to a piston and cylinder wall surface can be suppressed, so the injected fuel is liable to be vaporized; accordingly, it is possible to suppress the total amount (PN) of unburned particles and the number of unburned particles, which is the number thereof. In an engine that performs split injection, it is necessary to inject dividedly into a plurality of times the fuel that has been injected at one time; therefore, in the fuel injection device, it is necessary to control a minute injection amount as compared with the conventional fuel injection device. Further, in multistage injection, it is easy to obtain the effect of suppressing the number of unburned particles by increasing the number of injections; therefore, improvement of responsiveness of the fuel injection device and reduction of interval of fuel injection during the combustion stroke are required.
Generally, the injection amount of the fuel injection device is controlled by a pulse width of an injection pulse output from an engine control unit (ECU). A normally closed electromagnetic fuel injection valve (electromagnetic fuel injection device) has biasing means for generating a force in a valve closing direction. A drive portion includes a coil, a core and a mover. By supplying a current to the coil, a suction force is generated between the core and the mover. When the suction force exceeds the force in the valve closing direction, a valve body separates from the valve seat and a valve opening starts. Subsequently, by stopping the current supply to the coil, a valve closing starts when the suction force generated between the core and the mover decreases and becomes smaller than the force in the valve closing direction. Generally, in order to quickly shift from the closed valve state to the valve open state, a drive circuit of the electromagnetic fuel injection device first applies a high voltage from a high voltage source to the coil when the injection pulse is output, and then performs control to rapidly raise the current of the coil. Thereafter, after the mover moves away from the valve seat and moves in the direction toward the core, switching control is performed so that a constant current is supplied to the coil by switching the application of the voltage to a low voltage. In many cases, the high voltage source stores the voltage of a low voltage source; however, in the case of performing re-injection of fuel under a condition that the injection interval of a multistage injection becomes small and the voltage value of the high voltage source does not return to the initial value, a current value flowing through the coil varies depending on a difference in the voltage applied to the coil, and the injection amount variation may occur even under a condition of supplying the same injection pulse width.
As a means for suppressing variation in the injection amount as described above, there is a method disclosed in Patent Literature 1. Patent Literature 1 discloses a control method that estimates a voltage applied to a coil and lengthens a command injection period according to a decrease amount when the estimated value is lower than a specified value.
Further, for example, Patent Literature 2, discloses a control device of a fuel injection device that measure a time Tp from the start of energization until a current reaches a peak current value, and delays the energization stop by a delay time than the falling time of an injection command signal, as the amount of time Tp is longer than the reference value.